> > > I'd like to perform fully-automated incremental backups of my
> > > primary (C:) drive (excluding C:\Windows) every night at midnight.
>
I don't think ZTree is particularly suited to performing unattended batch tasks. It is better to use a command line utility. There is a well-established small reliable free command line utility called robocopy, that has a specific command line switch for performing an incremental backup. Its syntax is a bit weird, but once you have mastered it you can easily perform very sophisticated tasks.
I have for years used it to make a weekly copy of my main data drive to an external hard drive. For additional security I use two external hard drives alternately. I start the copy manually but then leave it to do its stuff.